So when a player is linked to hGH, as Orioles outfielder was by an SI.com report, many presume the player was desperate to bulk up and power baseballs into the stands.
"What athletes are doing is probably unlike anything we see in a clinical setting, so we don't know what it does," said Dr. Mary Lee Vance, a professor of internal medicine at the University of Virginia who wrote a 2003 study of growth hormone. "But the point is that none of our studies of aging populations have demonstrated measurable benefits other than to body composition."
Vance said it's possible that hGH, used in conjunction with high-intensity workouts, builds strength. But unlike with anabolic steroids, those benefits are perceived, not proven. Steroid use increases muscle mass disproportionately to overall body size. Growth hormone increases overall thickness, from muscle to bone to hair.
"If you take steroids and work out, you will get bigger and stronger," said Will Carroll, who writes about sports medicine issues and studied performance-enhancing drugs for his 2005 book The Juice. "If you take hGH and work out, there's no real clear evidence that you'll get stronger than you would have if you had just worked out."
That also was the conclusion reached by a 2004 survey of research on the subject in the American Journal of Sports Medicine.
Some athletes, including St. Louis Cardinals outfielder Rick Ankiel and New England Patriots safety Rodney Harrison, have said they turned to growth hormone to recover from injuries.
"That's the only reason guys take it," said former Orioles first baseman David Segui, who has said he took hGH on advice from his doctor. "People think guys are living on it, and that's not true. People don't want to hear this, but you don't get bigger and stronger off it. You don't get that big steroid look, that bulky look."
Perception vs. realityVance questioned athletes' belief in the substance's healing power.
"I think the key word is perception," Vance said, "because there's no evidence at all that it helps anyone recover from injuries."
Dr. Bill Howard, founder of the sports medicine clinic at Union Memorial Hospital, isn't so sure. He noted research on animals suggesting that growth hormone can help heal micro-injuries to the muscles. Such effects could help an athlete attempting to rehabilitate an injury, he said.
"It's the trendy, untestable drug, so that perception is a big reason why guys are going to take it," he said. "But I don't think their belief in it is unfounded. I think it does help you continue with hard workouts when it might be harder to do so otherwise."
Howard said hGH probably isn't as effective a strength builder as anabolic steroids.
Dr. Gary Wadler, a professor at New York University and member of the committee that determines banned substances for the World Anti-Doping Agency, agreed. But he suspects many athletes use it in tandem with low doses of testosterone, which could strengthen muscles made larger by hGH. SI.com reported that Gibbons received testosterone, as well.
"I think that many dopers are using several substances in combination," Wadler said. "And the science suggests that can be effective."
The negative effects of hGH are better established, researchers agreed.
Heavy users might quickly experience carpal tunnel swelling in the hands, and long-term use can lead to heart disease, diabetes and debilitating joint swelling, Vance said.
Gibbons is the latest athlete alleged to have received prescription performance-enhancing drugs from Orlando, Fla.-based Signature Pharmacy. The names have trickled out since February, when New York investigators raided the pharmacy in connection with an Albany County district attorney's investigation of an Internet steroid ring.
Other athletes linked to the investigation by news sources include Ankiel, Harrison, Toronto Blue Jays third baseman Troy Glaus, former Orioles outfielder Gary Matthews Jr., former Orioles second baseman Jerry Hairston Jr. and at least 11 professional wrestlers.
Investigators allege that athletes and dozens of other clients obtained prescriptions from doctors, some of whom lacked up-to-date licenses, and then ordered performance-enhancing drugs online from pharmacies such as Signature.
As the steroid cloud began to loom over baseball, fans associated possible use with sluggers who had bulked up mid-career. But Gibbons, Ankiel and Glaus are linked more by long histories of injuries.
Gibbons missed 65 games because of injuries during the 2004 season, when he allegedly bought testosterone and growth hormone. Glaus missed large portions of the 2003 and 2004 seasons because of a shoulder injury. His alleged steroid purchases fell between September 2003 and May 2004, according to SI.com. Ankiel, responding to a report in the New York Daily News, said he received a medical prescription for hGH to help him recover from reconstructive elbow surgery in 2004.
"The connection I see between these guys is desperation," Carroll said. "Whether it's desperation to recover from an injury or desperation to earn a contract, the risk becomes worth it."
hGH and injuriesUsers of hGH anecdotally report increased energy and ability to perform rehabilitation exercises in the wake of injury.
"It reduces inflammation and gets rid of the pain," Segui said. "But there's a misconception that it's about bulking up like what you see in the muscle magazines."
Some doctors believe hGH helps with recuperation.
"I'm not sure the research is in place," Wadler said, "but the general sense among people who deal with these issues is that it can be a reasonably effective recovery tool."
But not all agree. Vance said she prescribes hGH to patients with malfunctioning pituitary glands and to children whose bodies produce too little growth hormone naturally. Those, along with the treatment of frail AIDS patients, are the only legitimate uses for the substance, Vance said.
Researchers agree on the difficulty of detecting hGH. Growth hormone doesn't show up in the urine tests used by American professional sports leagues. Even in a blood test, synthetic hormone looks similar to the hormone produced naturally by the body. And none of the major sports unions has agreed to blood testing.
If enforcement officials dwell on hGH, however, they're missing the point, said Carroll, who said he believes athletes have moved on to a new generation of performance-enhancing drugs, such as insulin.
"It was the wonder drug a few years ago, and guys were flocking to it," he said of hGH. "But now it's almost beside the point. We don't learn what the state of the art is from the scientists. We learn from the users."
Sun reporter Roch Kubatko contributed to this article.